It has been known from the past that when a lens deviates from the optical axis, the eccentric error induces eccentric aberrations such as on-axis coma (producing a coma on the axis) or blurring on one side (i.e., the positions of foci formed by each off-axis light ray around an image plane are different in the direction of the optical axis) if on-axis light is used. Accordingly, the lenses are temporarily held to holding frames. The frames are mounted in a camera or lens barrel. Then, the eccentric aberrations in the whole lens system are checked. Based on the results, the eccentricities of the lenses from the holding frames can be adjusted.
For example, in the lens-centering mechanism described in JP-UM-A-5-36410, appropriate space is formed between the outer circumference of a lens and the inner circumference of a lens-holding member. Plural adjusting screws are tightened in from the outside of the holding member to bring the front ends of the screws into abutment with the outer circumference of the lens. Thus, the lens and lens-holding frame are temporarily held together. Based on the results of an inspection for eccentricities, the amounts of feeds of the adjusting screws are adjusted to center the lens and to position it. Then, an adhesive is injected through injection holes formed in the holding frames. In this way, the lenses are firmly held to the holding frames.
However, where each lens-holding frame is fabricated with a molding die for plastic injection molding, the die itself is expensive, because minute through-holes such as threaded holes and injection holes are accurately formed from the outer circumference of the lens-holding frame. Furthermore, the protrusions in the molding die for forming the through-holes tend to be easily damaged. There is the disadvantage that the mean time between failures (MTBF) of the die is short.
In addition, there is the danger that burrs are formed on the inside of threaded holes and injection holes in the lens barrel that is a molded product because of variations, for example, caused by environmental variations during molding process. If such burrs are produced, they are removed during assembly and become trash. There is the danger that the trash causes operational trouble or the trash is contained in the final image. Furthermore, when a lens is held to a lens-holding frame, the amounts by which plural adjusting screws are screwed in are adjusted simultaneously. Then, a test for eccentricity is performed. The lens is placed in the optimum position. Under this condition, an adhesive is injected. Therefore, plural screwdrivers for adjusting the adjusting screws and plural injectors for injecting the adhesive into the injection holes must be incorporated in the eccentricity-adjusting device. Consequently, there is the tendency that the eccentricity-adjusting device is increased in size. Furthermore, an operation for screwing in the adjusting screws and an operation for injecting the adhesive are necessary. In this way, laborious working steps have been required.